The present invention relates to a serial printer, particularly suited for the use in office typewriters. In the printer the printing characters are disposed on the extremities of flexible leaf springs, and provision is made of a selection mechanism positioning the character to be printed on the trajectory of a member pushing it against the paper.
In several printers known in the art as "wheel" or "chain" printers, the printing character, mounted at the extremity of a flexible leaf spring, is launched against the paper with a high velocity by an electromagnet. Because of the reduced mass of the character carrier and of the printing characters, such devices allow for a very fast positioning of the required character by means, for instance, of electronically driven step motors, reaching in this way high printing velocities. On the other hand the high velocity of the impact causes a very annoying printing noise, which is not acceptable today in a normal office environment. With such machines, to reach acceptable noise levels, it is necessary to use complex silencing enclosures, with narrow openings which besides being expensive, heavily limit the visibility and accessibility of the paper.
The produced noise is greatly reduced with the "non impact" printers, however the known types of solutions: ink-jet, thermal, electrostatic, electrochemical, etc., are not suitable for use in normal typewriters, because they are complicated and expensive, often they require the use of special papers, give a poor printing quality and do not allow the simultaneous obtaining of copies, which constitutes an indisposable requirement for normal office typewriters.
In some known typewriters of the hammer type, called "noiseless", it has been tried to reduce the noise produced by the printing by controlling the movement of the hammer in its trajectory against the paper, through the interposition of special kinematics between the key and the corresponding hammer, so that the hammer should meet the paper with a low velocity. Besides being complex and expensive, because of the multiplicity of the required mechanisms, such solutions are not very effective, because of the relevant mass and of the unavoidable play of the complex mechanism that accompanies each hammer in its run.
There are also known devices using printing balls or drums where it has been tried to reduce the printing noise by controlling the movement of the ball or of the drum against the paper, so that they meet the paper with a low velocity. Such devices have however inconveniences similar to those already indicated for the "noiseless" devices, because of the relevant mass and of the unavoidable plays of the ensemble represented by the ball or drum and by the mechanisms for their rotation and translation, that go along with them in their movement against the paper.
For the office typewriters the need is strongly felt to combine the simplicity, flexibility of use, ease of interchange of the printing characters, specific of the "wheel" and similar type printers, with the absence of noise of the non impact printers.